There are a few ways to get a Dark Fiend Monster on an opponents field
Sunken Field will outright ruin someone's plan if they don't take it into account
When the monster is level 7 or higher, they require two tributes
This is because she can heal 50 damage from any of your Grass-types as opposed to the Potion, which only heals 20
This ability means that, if characters named Dewey and Louie are also currently in play alongside Huey, then whenever Huey, Savvy Nephew quests you are able to also draw three cards, as well as gain a lore
And since the condition is "sent by GY with an effect", there is no need to break your jaw on the field, you can send it from the Deck to GY with the effect of "Battlin' Boxer Headgeared", and you can see a lot of Battlin' Boxer X monsters